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Observation Logs

Submitted by MikeK on Fri, 10/18/2013 - 14:29

As professional observers provide isoncampaign.org notes on their observing runs, we will add them to this page. Send your own brief observing notes via our contact form or directly to Mike Kelley (UMD). Observing reports are meant to highlight everyone's progress or struggles observing this comet, in order to aid and/or encourage future observations, and provide critical input for target of opportunity programs.

Karl Battams (NRL) provides some analysis of the post-perihelion observations of the comet with the STEREO A spacecraft's HI-1 instrument:

“A broad and diffuse remnant of comet ISON is still visible in the STEREO HI-1A images. Due to a complete lack of any kind of central condensation, photometry is impossible at this stage, but a good-by-eye estimate would be that the comet remnants continue to drop at approximately half a magnitude per day, and in the most recent images appear to be around magnitude +11. While the comet is expected to leave this field of view around December 7, 2013, we suspect it may fade below the instrument's ~ +13.5 limiting magnitude before this time.”

“Comet ISON has brightened dramatically since it entered the SOHO C3 (note that C3 is the name of the telescope, it is not referring to the molecule) field of view yesterday. In the clear filter images it had an apparent V magnitude of 2.5 on Nov 27.05 when it entered the field of view and has increased steadily in brightness to mag 0.5 on Nov 27.54. Note that it began saturating the detector soon after entering the C3 field of view and I am employing a correction that I developed for C/2011 W3 Lovejoy. This brightening behavior is similar to typical brightening by Kreutz comets in the SOHO fields of view.”

Karl Battams (NRL) provides further analysis of Knight's photometry:

“Based on the photometry, and the visual appearance of the comet in the SOHO LASCO data, we have updated the Current Status page to tell observers to plan for a negative magnitude object. A conservative estimate would be -1, but -3 or -4 is certainly reasonable at this point.

“ISON has continued to brighten in the STEREO-HI1A images over the last 36 hr. As of Nov 26.54 it is approximately a V magnitude of 3.9 in an 11.7 arcmin diameter aperture. Just looking at the lightcurve by eye suggests that there may have been an outburst from roughly Nov 20-22 which was superposed on a steadily brightening curve.”

“As of Nov 25.63 ISON has an apparent V magnitude of 4.4 in an 11.7 arcmin diameter aperture in STEREO-HI1A images. It has trended smoothly brighter over the preceding ~0.5 day. I have not noticed any significant difference in the coma morphology since my previous report.” (70 arcsec pixel scale)

“After Nov 7 it increased by factors of 2 every one to three days for the next two weeks. On Nov 16.6 and 19.6 we find a water production rate of 4e29 molecules/s followed by a factor of 5 increase to values about 2e30 molecules/s from Nov 21.6 to 23.6. ISON is now in the SWAN solar avoidance area until a few days after perihelion.”

“Comet ISON had an apparent magnitude of 4.3 in an 11.7 arcmin diameter aperture on Nov 20.97 as viewed by STEREO-HI1A (Δ=1.0 AU; approximately V magnitude).”

M.A. DiSanti and B. Bonev (NASA/GSFC) report on observations using CSHELL at the NASA IRTF telescope:

“We had photometric conditions for the last pre-perihelion day with CSHELL (solar elongation 20 deg). We focused on a continued deep search for HDO, but aspects of the volatile chemistry were also done (HCN, NH3, C2H2, C2H6/CH3OH), plus a re-visit of CO once the geocentric Doppler shift returned, passing +10 km/s around 21:30 UT. H2O was measured in three settings (including the CO setting) and we should have a handle on production rates soon.”

“Comet ISON had an apparent magnitude of 5.0 in an 11.7 arcmin diameter aperture on Nov 22.21 as viewed by STEREO-HI1A (Δ=1.0 AU; approximately V magnitude).”

Emmanuel Jehin and Cyrielle Opitom (Univ. de Liège) measured the comet with the STEREO A spacecraft's HI-1 instrument:

“We observed with TRAPPIST for the last time, ISON. It was 6 degrees above the horizon and clear sky. The comet is still intact showing the usual shape of the coma. After the outburst of 19 Nov, the Qs have stabilised yesterday morning and, from data taken today, may be dropping. The maximum of the outburst, Nov. 21.37: Q(OH) = 1.08 (+/- 0.58) x 10**29 molecules/s, Q(CN) = 1.60 (+/- 0.18) x 10**27 molecules/s, Q(C2) = 2.52 (+/- 0.12) x 10**27 molecules/s, Af(rho) = 5820 +/- 644 cm. Two bright jets perpendicular to the tail are visible and there is no indication yet of splitting or disruption.” (Opitom et al. 2013, CBET 3719)

“We observed arcminute spatial coverage of H20+, Na and C2 bands at a resolution of 30000. In wide-field imaging, the sodium tail grew significantly overnight between Nov 19th and 20th UT, then extending more than a full degree of sky.”

Emmanuel Jehin and Cyrielle Opitom (Univ. de Liège) report a new outburst of comet ISON, observed with the TRAPPIST telescope:

“Since last night (Nov 19) comet ISON is getting brighter again! After the drop of the last 5 days, all the Qs have been x ~5 in about 48 hours. This looks to be a new outburst linked to the active regions, as the jets are today strong again. We hope to be able to point the comet again the next 2-3 nights, at 10 deg above the horizon during nautical twilight.”

“Between 17:00 and 23:15 UT, the comet was observed with high spectral resolution (R ~ 22,000) in eight grating settings between 2.84 and 5.00 microns. The following species were detected: H2O, OH, NH3, NH2, HCN, CN, C2H6, C2H2, CH3OH, H2CO, and OCS. A preliminary analysis indicates a water production rate between about 1.5 and 3e29 molec/s. Determination of abundances relative to H2O and any productivity variation over the observing time period are in progress.”

“The MESSENGER spacecraft has successfully imaged and obtained spectra of both Encke and ISON during their closest approaches to Mercury. Much of the data remains on the spacecraft awaiting downlink, but we have confirmed detections of H, O, C, S, OH, CS, and NH with the MASCS instrument for both comets. A press release with images and more information has been released.”

“We have found another wing feature in the coma of comet ISON in images taken in the morning hours of 18 Nov. at the Mt. Wendelstein Observatory. This may indicate a second nucleus splitting. The diffuse wing structure from the previous event was also found in the same images, and it appeared more diffuse and much weaker than the days before. We would like to encourage imaging of the comet over the coming hours and days/nights as much as possible in order to follow the evolution of the features related with the new and old event of enhanced activity in this comet.”

B. Bonev and M.A. DiSanti (NASA/GSFC) report on observations using CSHELL at the NASA IRTF telescope:

“We observed comet C/2012 S1 (ISON) on UT 2013 Nov. 15, 16, 17, 18, and 22. Multiple primary (parent) volatiles were detected, including H2O, C2H6, CH3OH, CO, HCN, NH3, C2H2, and possibly CH4, plus two fragmentation products (NH2 and OH). Based on 7 spectral lines of H2O and assuming an atmospheric seeing correction (growth-factor) of 1.8, the global water production rate varied between about 1.2 and 2.6 (E29 molecules/s) during the Nov. 15-18 time frame. The possible role of short-term variability in production rates, such as could be produced by nucleus rotation, is under consideration. On UT Nov. 17 (R_{h} = 0.53 AU; Delta = 0.87 AU) we oriented the slit along the Sun-comet line (position angle = 289 degrees, as projected on the sky plane) and measured spatially resolved rotational temperatures (Trot) and column densities for H2O. We observed a decrease in Trot with nucleocentric distance, from 115 K near the position of peak emission intensity to around 90 K at projected distances offset by about 1000 km. (All results are preliminary.)” (Bonev et al. 2013, CBET 3720)

“HCN measurements over Nov 15, 16, and 17 do show real variability. We also detected a decrease in the intensity of the HCN 4-3 line through out the day of Nov 17th. Other observers, IRTF and APEX, informally noted this behavior and our data sets agree. Our team will be observing again around perihelion.”

“CN, CH, C2, C3, NH2 emissions were identified, as well as some other lines. It is expected that the ratio 12C/13C will be constrained, perhaps 14N/15N, and maybe D/H. O, He, and Na emissions were also identified.”

“Water production rates derived from the Lyman-alpha observations assuming it comes from water dissociation have jumped by a factor of 5 during Nov 13 - Nov 15.” (This text has been superseded by the report on Nov 24.)

“Spectroscopy of C/ISON with a spectral resolution of R=30-120 were obtained on 11 & 12 Nov. using The Aerospace Corporation's Broad-band Array Spectrograph System (BASS). The spectra exhibited a weak silicate emission feature, being only 10% or less above the underlying continuum. The integrated brightness of the 12th was ~40% brighter than on the 11th, indicating the recent observed outburst was being detected at thermal-IR wavelengths. The observation were made during periods 1-2 arcsec seeing, and in breaks in fog and ice at the summit of Mauna Kea.”

N. Dello Russo (JHU/APL) reports on an observing run using NIRSPEC at the Keck telescope:

“No observations were obtained on C/2012 S1 ISON on UT Nov 11 and 12 at the Keck Observatory due to poor weather.”

“Water production rates derived from the Lyman-alpha observations assuming it comes from water dissociation showed a rather flat variation from Oct 25 to Nov 7, around 2e28/s - 2.5e28 molecules/s, and then back down to 2e28 molecules/s by Nov 7. Between Nov 7 and 9 it jumped by a about a factor of 2. Because of the lifetimes of H2O and OH combined with the large SWAN field of view, changes in Q-water normally take 1 to 3 days to be seen in H.” Nov 26 update: “The water production rate... remained between 2e28s and and 3e28/s from Oct 24.9 to Nov 6.9. After this it increased by factors of 2 every one to three days for the next two weeks.”

Ron Vervack (JHU/APL) observed the comet with the NASA IRTF and SpeX for a third night:

“Our program's final set of pre-perihelion SpeX observations of ISON was done today. We got prism and LXD mode spectra again, and the comet has clearly started to show more thermal emission from the dust. The continuum above 2.9 μm was easily seen compared to essentially nothing on October 17 and 28. For the first time, there are hints of gas emission, mostly CH3OH near 3.52 μm though there could be also some of the regular IR emitters spread about that further analysis may tease out. Conditions continue to be mediocre overall.”

“The visible light continuum within ~220 km of the nucleus varied by a factor of ~2 in brightness with an apparent period of ~10.4 hr, although the sparse sampling of the light curve indicates that periods within the range 8-12 hr give acceptable fits to the observations. The gaseous emissions from OH and CS also varied significantly during the course of the Hubble observations. From the emission in the OH(0,0) band, we derived Q[H2O] of 2.4e28 on Nov 1.372 UT and 2.1e28 on Nov 1.571 UT. CO did not significantly vary in two measurements of the fourth positive group near 150 nm. From these data we derive Q[CO] of 2.7e26, which gives a CO/H2O abundance ratio of 1.1-1.3%.” (see also, Weaver et al. 2013, CBET 3680)

Ron Vervack (JHU/APL) again observed the comet with the NASA IRTF and SpeX:

“Spectra in both the prism and LXD modes of SpeX were acquired on ISON again. The comet has brightened, but between the weaker than expected productivity at this point and only fair observing conditions, no gas emission was conclusively detected. Continuum below 2.5 μm is obvious and should be useful.”

Mike Kelley (UMD) reports on optical imaging polarimetry of comet ISON with the University of Minnesota's Mount Lemmon 60" and OptiPol instrument. He writes:

“Weather was clear for three nights. We obtained about 40 minutes each of R-band images on two nights, and I-band images on a third. The comet was too faint for our narrow-band red filter (0.68 +/- 0.01 μm). The coma is peaked at the center, similar to the recently released Hubble Space Telescope images, suggesting a 1/ρ coma continues to persist.”

“The spectra, taken 18 - 21 Oct. using the SpeX spectrograph's prism disperser, spanning 0.8 - 2.3 μm, indicate that that the spectrum of C/ISON is redder than the solar spectrum. The recent spectra indicate that the flux of the comet is larger in October 2013 by a factor of nearly 4, compared to the measured flux on 11 September 2013 (UT), by M. Sitko and R. Russell. The October measurements are part of the IRTF's Comet ISON Observing Campaign. ”

Ron Vervack (JHU/APL) reports that near-infrared low resolution spectra of comet ISON with the NASA IRTF and SpeX were successful, through high humidity and spotty clouds. He writes:

“Prism images look good, with a reasonable signal-to-noise ratio. In the LXD images, continuum is generally easy to see up to the big water gap starting at 2.5 μm. The continuum is fuzzy with no sharp center. Beyond the gap, the continuum is much more difficult to see. It's there, but it's faint. No obvious gas emission in stacked raw data. Guiding on the comet with SpeX worked well. The integration time had to be long (10 seconds) at the start to see much, and we had to subtract a background sky.”

Blog archive

Image of the Week

Every week, a new image related to Comet ISON!

This week: The Final Nail in the Coffin? When ground-based observers came up empty-handed in the hunt for ISON's remains, we turned to the Hubble Telescope to see if its ultra-powerful instruments could find anything...Earlier picks can be found in the ISON Image of the Week Archives. Note that this feature will become monthly, instead of weekly, in 2014.